Technical Field
The present disclosure relates to an organic light-emitting diode (OLED) display and a method of manufacturing the same. More particularly, the present disclosure relates to an OLED display capable of reducing bubbles (foams) in an interface between an upper inorganic layer and a lower inorganic layer, and a method of manufacturing the same.
Description of the Related Art
An organic light-emitting diode (OLED) display is capable of producing light on its own and thus does not require an additional light source, unlike liquid crystal displays (LCDs). Therefore, OLED displays can be made lighter and thinner than LCDs. Further, an OLED display has advantages in that it is driven with low voltage to consume less power, and is capable of reproducing vivid colors, has a fast response time, wide viewing angle and infinite contrast ratio (CR). For these reasons, an OLED display is currently under development as the next generation display device.
OLED displays employ a light-emitting layer made of an organic material and thus are very sensitive to moisture, oxygen and etc. Accordingly, in order to suppress oxygen and moisture permeation into the organic light-emitting layer, various techniques for sealing or encapsulating an organic light-emitting element are used.
For a top-emission OLED display in which light generated in an organic light-emitting layer is emitted toward the top direction, a sealing element is required to have a certain degree of transparency. Accordingly, glass is typically used as the sealing element since it is easily available and has high transparency. However, as flexible OLED displays prevail in recent years, there have been attempts to replace glass having low flexibility with an inorganic layer as the sealing element.
Although a thin, single inorganic layer has high transparency and flexibility, cracks or other defects may occur if the inorganic layer is repeatedly bent. Since moisture may permeate through cracks created in the inorganic layer, the single inorganic layer cannot effectively suppress moisture from permeating the organic light-emitting layer.
To overcome this shortcoming, a thin film encapsulation technique in which inorganic layers and organic layers are alternately stacked on one another to seal the organic light-emitting element has been proposed. According to the thin film encapsulation technique, an organic layer for compensation of cracks caused by bending, stress, foreign matter, etc. and for leveling step differences is formed on an inorganic layer, and then another inorganic layer is formed on the organic layer. Since an organic layer cannot effectively suppress moisture permeation, edges of an upper inorganic layer come in contact with a lower inorganic layer such that the upper inorganic layer completely covers the organic layer, thereby suppressing moisture from permeating the organic layer.
As a material for inorganic layers in the thin film encapsulation technique, silicon nitride (SiN) has been commonly used. However, in order to improve performance characteristics of top-emission OLED displays, inorganic layers having better barrier property and high transparency for use in the thin film encapsulation technique need to be developed.